Oracle Database Administration I — Question 49

Which two statements are true regarding the UNION and UNION ALL operators? (Choose two.)

Answer options

• A. Duplicates are eliminated automatically by the UNION ALL operator
• B. The number of columns selected in each SELECT statement must be identical
• C. The names of columns selected in each SELECT statement must be identical
• D. The output is sorted by the UNION ALL operator
• E. NULLS are not ignored during duplicate checking

Correct answer: B, E

Explanation

The correct answer B is true because both SELECT statements must have the same number of columns for the UNION and UNION ALL operators to work. Option E is also correct because NULLS are included in the duplicate checking process. Options A, C, and D are incorrect as UNION ALL does not eliminate duplicates, column names do not need to match, and the output is not automatically sorted by UNION ALL.